Added error checking on linesearch

specific/optimization/localminimumsearch/classic.cpp

@@ -79,6 +79,13 @@ namespace classic
         msg::print << "Search minimum (classic)" << msg::endl;
         msg::indent();
 
+        if (!linesearch) {
+            throw Exception("No linesearch provided.");
+        }
+        if (!descentsearch) {
+            throw Exception("No descentsearch provided.");
+        }
+
         descentsearch->initialize(functional);
 
         std::vector<LocalMinimumSearchHistoryLine2> historyline;